Chemistry-Grade-nine- Revision-for the coming exam.ppt

grade nine chemistry for exam preparation

1. Concepts
in G-9
Chemistry

2. CHEMICAL BONDING +
INTERMOLECULAR FORCES
CEMICAL BONDING
•Define chemical bonding + explain why atoms
form chemical bonds
–A chemical bond is any attraction b/w 2 particles
–This particles may be atoms, ions, or molecules
–Atoms form bonds to achieve a more stable electron
arrangement – a full outer shell of electrons
–This can be achieved by:
•Transferring one or more electrons – ionic bonding
•Sharing one or more pairs of electrons – covalent bonding

3. CHEMICAL BONDING +
INTERMOLECULAR FORCES
CEMICAL BONDING
•Define chemical bonding + explain why atoms
form chemical bonds
–Energy changes occur during bond formation – make
it more stable
–Atoms having a full outer shell of electrons – elements
in G-8 (noble gases) – have little chemistry as they
don’t readily form bonds

4. Ionic bonding
•Explain the term ion
•Illustrate formation of ions by giving examples
•Define ionic bonding
•Describe the formation of ionic bond
•Give examples of simple ionic compounds
•Draw Lewis structures or electron-dot formulas
of simple ionic cpds
•Explain the general properties of cpds

5. Ionic bonding
•Ion is an atom which has lost or gained one or
more electrons
•Metals tend to lose electrons to form +vely
charged ions or cations
•Non-metals tend to gain electrons to form –vely
charged ions or anions
•Hydrogen forms both a cation, HH
++
(hydrogen
ion), and an anion, HH
--
(hydride ion)

6. Ionic bonding
•Relate the position of elements in the periodic
table to the normal ion formed by them:
Group 1 – M
++
e.g. Na
++
Group 2 – M
2+ 2+
e.g. Mg
2+2+
Group 3 – M
3+ 3+
e.g. Al
3+3+
Group 5 – X
3-3-
e.g. N
3-3-
Group 6 – X
2-2-
e.g. O
2-2-
Group 7 – X
--
e.g. Cl
--

7. Ionic bonding
•Writing the formulas of ions formed by atoms
of d/t elements
–The easiest way for a metal to achieve a full outer shell of
electrons is by losing electrons
•E.g. sodium atom (2,8,1) >>>>> sodium ion (2,8)
–Similarly the easiest way for a non-metal to achieve a full
outer shell of electrons is by gaining electrons
•E.g. chlorine atom (2,8,7) >>>>>> chloride ion (2,8,8)

8. Ionic bonding
•Ionic bond - is the result of forces of attraction
between oppositely charged ions
•Formation - ionic bond is formed by the transfer
of one or more electrons from a metal atom to a
non-metal atom
•Represent the formation of an ionic compound
using Lewis structure and symbol
•When forming ions, the name a non-metal takes
the ending – ide
–e.g. nitride, oxide, chloride

9. Ionic bonding
•General properties of ionic compounds:
–Crystalline nature
–High melting points and boiling points
–Ability to conduct an electric current when molten or in
aqueous solutions
–Solubility in polar solvents like water

10. Covalent bonding
•Define covalent bonding
•Describe the formation of a covalent bond
•Draw Lewis structures or electron-dot formulas of simple
covalent molecules
•Give examples of d/t types of covalent molecules
•Explain polarity in covalent molecules
•Distinguish between polar and non polar covalent molecules
•Define coordinate covalent (dative) bond
•Illustrate the formation of coordinate covalent bond using
suitable examples
•Explain the general properties of covalent compounds

11. Covalent bonding
•Covalent bonds are formed when atoms shared pairs of
electrons
•The bond arises due to the electrostatic attraction b/w
the –ve electrons & the +vely charged nuclei of the two
atoms
•Covalent bonds are generally formed b/w atoms of non-
metals
•Gaseous elements in Groups 5, 6, & 7 exist as
molecules joined by covalent bonds. e.g. N
2
, O
2
, CL
2
, F
2.
•Drawing Lewis structures for common covalent
compounds

12. Covalent bonding
•Covalent bonds are formed when atoms shared pairs of
electrons
•The bond arises due to the electrostatic attraction b/w the –
ve electrons & the +vely charged nuclei of the two atoms
•Covalent bonds are generally formed b/w atoms of non-
metals
•Gaseous elements in Groups 5, 6, & 7 exist as molecules
joined by covalent bonds. e.g. N
2
, O
2
, CL
2
, F
2.
•Drawing Lewis structures for common covalent
compounds
–E.g. HCl, H
2
O, NH
3
, CH
4

13. Covalent bonding
•In some covalent compounds, atoms are joined by double and
triple bonds:
C–C(ethane), C=C(ethene), C≡C(ethyne)
In gases: N≡N, O=O
C=S, C≡N
•Sharing of the pair of electrons in covalent bond depends on
attraction w/c each atom has for the electrons, related to EN of
atom
•Sharing of the pair of electrons in molecules b/w 2 atoms of
same element, or 2 atoms of similar EN:
–Electrons are attracted equally by the 2 atoms
–The electron pair is shared equally

14. Covalent bonding
•Sharing of the pair of electrons in molecules b/w 2 atoms
of d/t EN e.g. HCl:
–Cl atom is more EN than H atom
–Cl atom attracts the electrons in the covalent bond
more strongly
–The Cl end of the bond is slightly –ve relative to H end
–The relative charge is shown using the symbols δ
+

and δ
-
–The bond is polarized and shown as H
δ+
Cl
δ-

– identify polar & non polar bonds in covalent cpds

15. Covalent bonding
•Coordinate covalent or dative bond
–Type of covalent bond in which both of the electrons which form a
covalent bond b/w atoms is donated by one of the atoms
–E.g. H
3O
+
, NH
4
+
,

CO
•Lone pair – a non-bonding pair of electrons
•General properties of covalent compounds:
–Liquids or gases, some are solids
–Low melting and boiling points
–Do not conduct an electric current when molten or in aqueous
solution
–Solubility in non-polar solvents
–Insolubility in polar solvents like water

16. Metallic bonding
•Explain the formation of metallic bond
•Explain the electrical and thermal conductivity of
metals in relation to metallic bonding
•Metals:
–Consist of a matrix of +vely charged ions in a sea of
delocalized electrons
–Able to lose valence electrons so easily
–Ability to conduct both heat & electricity (related to mov’t
of delocalized electrons)
–These are able to transfer energy & charge via the metal

17. Metallic bonding
•Metallic bonding is the result of electrostatic
attraction between the +vely charged metal ions
and the –vely charged delocalized electrons
•The strength of metallic bond is related to the
atomic radius of metal the atom & the no of
valence electrons (delocalized)
–Metallic bond is strongest where metal have
small atomic radii & lose a large number of v.e.
•Malleability and ductility

18. Intermolecular forces
•Define IMF
•Explain hydrogen bonding
•Explain the effects of hydrogen bond on the
properties of substances
•Describe Vander Waals forces
•Explain dipole-dipole force
•Give examples of molecules with dipole-dipole forces
•Explain dispersion forces & give examples
•Compare and contrast the 3 IMF

19. Intermolecular forces
•IMF is a force of attraction b/w molecules in a
substance
•Hydrogen bond is an IMF of attraction b/w a highly
polar hydrogen atom on one molecule & highly EN
atom on another
•Hydrogen bonding is the strongest of the IMF
•The O–H bonds in water are polar due to the high
EN of oxygen.
•Water molecules are attracted each other.
•This attraction gives rise to hydrogen bonding

20. Intermolecular forces
•Effects of hydrogen bonding on the properties
of water include:
–High melting & boiling points
–Surface tension
–Formation of a meniscus
–Capillarity
–Coolant (in radiators)
•There are always forces of attraction b/w
covalent molecules even if they are polar or not

21. Intermolecular forces
•Van der Waals forces are weak electrostatic
forces that bind both polar & non-polar molecules
• they may be:
–Dipole-dipole forces
–Induced dipole-induced dipole or dispersion forces
•A dipole is two points of equal but opposite
charges, separated by a distance
•Dipole exist in polar molecules & oppositely
charged ends of dipoles on d/t molecules are
attracted to each other

22. Intermolecular forces
•Dispersion forces occur in non-polar molecules
•They are the results of temporary fluctuations in
electron density
•Within any bond, a slight temporary mov’t of bonding
electrons towards one or other of the atoms will
cause an induced dipole.
•This will result in molecules being attracted to each
other
•Examples: Ne, CH
4,
•Dispersion forces exist in all types of molecules

23. Exam Topics
•All Notes (from notes, worksheet and homework)
•Vocabulary Text Pages (6-9)
• Branches of Biology
•Levels of Organization (13)
•History of Humans and Scientists
•Safety Symbols (from binder)
•Scientific Method (short version)
•7 Features of Living Creatures (GSMC MRI)
•Neanderthal Video
•Worksheets (Analyzing Science Words w/ added prefixes,
Neanderthal Video questions, Branches of Bio)
•NO MICROSCOPE STUFF and NO GEOLOGICAL TIME
SCALE STUFF INCLUDED ON THIS TEST